I ran a couple of times into the same exact issue and each time it took me a few hours to find a solution.

When you’re embedding a custom map from My Places (in Google Maps) as an iframe, and your links in Info Windows/Blurbs open up in the same iframe, rather than in a new or same window, here is what you need to do.

In case the above link stops working or content disappears, I’m re-posting the solution below:

So: maps.google.com, I clicked on “My Maps”, then clicked on the map I want to fix. On the top right side there is a Google Earth link. I *right* clicked on it and copied the URL.

Then, on maps.google.com, in the search input textfield, I pasted the url and clicked ‘search’.

On the right side of the window, I clicked on “Link to this page”, and copied the new html code and pasted it into my website, instead of the old one.

With this solution, when you click on a link inside the map, it opens in a new tab. It’s not the best behavior, but it’s better than opening in the iframe. And people can still edit the old map and modifications will be automatically displayed in the new map.

However there is another problem with this solution: your markers must be 32×32 pixels, otherwise they will be resized.